Electricity and other forms of energy are billed in accordance with energy consumption that may vary with the size of the customer and the time of day. Since the peak amount of energy consumed by a customer over a given time period (so-called "demand") determines the size of the service required, e.g. size of conductors, transformers, peak generating capacity, etc., many utilities measure this peak consumption or demand to determine the rate to be charged the customer for all electricity consumed over a given period.
To determine the amount of energy being consumed by each customer during successive demand intervals, utility companies have located, at customer sites, electricity meters, such as watthour meters containing a demand register, which must periodically be read either by the customer or by a representative of the utility, to accumulate billing data (e.g. peak demand and total energy consumed). In addition, to evaluate customer energy demand so as to assess the capability of the utility's equipment to satisfy demand, or to justify rate modification, energy demand occassionally must be surveyed over an extended period of time, e.g. 18 months.
Electrical demand is typically measured by the use of a pulse initiator which utilizes a photo-optical detector to detect the rotation of the eddy-disk of a watt-hour meter and produces a series of pulses whose frequency is directly related to the instantaneous power (demand) being delivered to the customer.
Typically, a demand register accumulates these pulses over a preselected interval, e.g. 15 minutes, to give an indication of the peak demand over the interval. This peak demand data is then stored in a memory device for subsequent readout or display.
Since there will often be large numbers of meters registering demand throughout a utility system there exists a need to monitor electrical demand simultaneously at a large number individual customer sites, and to process the data at a central location. This is commonly done by means of a mainframe computer operated by the utility company. This information is used by the utility to assess demand parameters such as peak demand and seasonal as well as daily demand variations. Accordingly, systems have been developed for polling customer meters to extract and transmit energy demand data over commercial telephone lines to the central computer for accumulation and processing.
Because the investment required to provide automatic polling of remote meter registers at the the customer site is substantial, as an alternative, automatic meter data recorders have been developed that are set up at customer sites to be monitored. The data recorders commonly employ magnetic tape storage techniques to record pulses generated by the pulse initiator of the meter that represent electrical demand during successive intervals. The magnetic tape is then carried to the utility for processing.
Magnetic tape recorders of the type employed for this purpose are relatively complex, require substantial battery power to operate in the event of a power failure and may fail to work properly in environments exposed to temperature extremes. Recently, due in part to availability of inexpensive solid state memory devices, portable meter reading devices having solid state memories have been developed for accumulating demand data stored in a meter. The reading device is then either brought to the central computer and the data transmitted directly to the computer, or the data is transmitted over telephone lines to the central computer. There is a tendency, however, for errors to occur in the acquisition and transmission of data. These errors are caused by among other things failures of the solid state memory, misdetection of pulses generated by the electricity meter and, most commonly, electrical noise contamination. Data acquisition errors are particularly troublesome because they affect, among other things, the accuracy of customer billing. For this reason there currently exists a significant need to verify energy demand data accumulated from customer meters to ensure that the data is accurate. Also, since peak demand data must be correlated with the time of day, day-of-week, season, etc. for proper billing purposes, it is necessary that such a data acquisition device be capable of operation despite power outages occuring on the powerline.
One object of the invention, therefore, is to provide a method of and system for verifying data accumulated from remote electricity meters during successive demand intervals and to confirm that the data measured represents data upon which a utility company or other controlling institution can rely. Another object is to provide a relatively inexpensive and reliable device for making energy demand measurements and verifying their reliability at customer meter sites for the purpose of obtaining demand survey and customer billing data. A further object is to provide an electricity demand data acquisition device which operates reliably even during a power outage.